The present invention relates to gear synchronizer mechanisms and, more particularly, to strut-type synchronizers having reduced drag force for promoting improved shift feel.
In general, conventional strut-type synchronizers include a plurality of key-like struts which are normally biased into engagement with a circumferential detent groove formed in the internal splined surface of the shift sleeve. Axial displacement of the shift sleeve causes the struts to energize the synchronizer mechanism for blocking further axial displacement of the shift sleeve until speed synchronization is complete. For example, U.S. Pat. No. 4,566,568 issued Jan. 28, 1986 to Yant discloses a strut-type synchronizer having a leaf spring member radially interposed between the hub and the shift sleeve which is adapted to bias the strut radially outwardly into engagement with the detent groove formed in the inner bore of the shift sleeve.
U.S. Pat. No. 4,770,280 issued Sept. 13, 1988 to Frost and assigned to the common assignee of the instant application discloses a strut-type blocking synchronizer mechanism which is incorporated into a vehicle transfer case for shifting from a two-wheel drive mode to a four-wheel drive mode. The synchronizer mechanism includes a pair of energizing retainer springs acting to radially outwardly bias the struts confined within slots in the hub into engagement with the detent groove. Likewise, U.S. Pat. No. 4,445,602 issued May 1, 1984 to Chana discloses a similar strut-type synchronizer arrangement utilized in a manual transmission.
A principle drawback associated with most conventional strut-type synchronizers however, is poor "shift feel" when compared to strutless type synchronizers. This is due largely to the excessive drag forces generated by the energizing springs for maintaining biased engagement of the struts and the shift sleeve splines upon continued axial movement of the shift sleeve following completion of speed synchronization. Currently, the vehicle operator must physically overcome this frictional drag force by exerting a greater counteracting force to the gear shift lever for completing the gear shift. As such, the vehicle operator is unable to advance the gear shift lever smoothly to complete gear lock-up without experiencing some undesirable shifting resistance.